Rocks, soils and fossils
Chemistry · Key Stage 1 · The School
Testing rocks properly
Rocks differ in hardness (does a nail scratch it?), grain size (can you see the crystals?) and whether they soak up water. Test several the same way and record in a table. Chalk crumbles and soaks; granite resists both — which is why one makes cliffs that wear away and the other makes kerbstones.
How a fossil forms
An animal dies and is quickly buried in mud or sand — quickly matters, or it rots away. Soft parts decay; hard parts stay. Over millions of years the sediment turns to rock and minerals replace the bone, keeping its shape. So a fossil is not the bone: it is stone in the shape of a bone.
Soil is a mixture
Soil is broken rock plus dead plant and animal material (humus) plus water, air and living things. Shake soil with water in a jar and let it settle: heavy stones sink first, then sand, then clay, with humus floating on top. The layers show you what your soil is made of in about ten minutes.
Take chalk, slate and granite. HARDNESS: try scratching each with a coin — chalk marks easily, granite not at all. GRAIN: look with a magnifier — granite has big visible crystals, slate is fine and flat. PERMEABILITY: drop water on each — chalk soaks it in, slate and granite let it sit. Three tests, the same three rocks, and the results are what a geologist actually uses to identify them.